The only things that are available at certain levels are the Dropped Sets. Otherwise the differences are the material that makes the weapon/armor changes as you go up in levels. But, in that case it's still an Axe or Sword or a Jerkin.
Here is some information on the Dropped Sets. It may not be completely up to date with the stats, but it is the best list I have found
Then there are the crafted sets that you need to learn Traits to make. Those can almost be used at any level, but at lower levels you get less bonuses. I think some are even level locked in that you can't even make them for a low level (like L10 or less or whatever, but they are sets you need to know a lot of traits to make) Nice thing is, some of the best sets you can make only require 2 to 4 Traits, although there are some sweet 5 and 6 trait sets.